For many years decorative laminates have been used as a surfacing material in residential and commercial structures wherein aesthetic effects, in combination with functional behavior such as wear, heat and stain resistance, are desired. Such decorative laminates generally are produced from a supporting base member such as a plurality of core sheets usually composed of kraft paper which has been impregnated with a thermosetting resin and, more particularly, with a thermosetting water-soluble or water-insoluble phenolic resin. When the kraft paper has been impregnated with the thermosetting resin, the sheets are dried and cut to the appropriate size. Thereupon, a plurality of these resin impregnated sheets are stacked in a superimposed relationship. The number of plies or sheets in the stack depend on the ultimate intended use of the laminate. For most purposes, the number of plies of these core sheets will total about six to nine but can total as many as 12-15.
There is then placed on the stack of core sheets a decorative sheet which is generally an opaque, pigmented sheet of alpha-cellulose paper and is impregnated with a noble thermosetting resin which is not subject to significant darkening upon the application of heat. Suitable resins for the decorative sheets are the aminotriazine resins and more particularly the melamine-formaldehyde resins, the benzoquanamine-formaldehyde resins, the unsaturated polyester resins and the like. Often the decorative sheet carries a printed pattern design on its surface. It is generally desirable when making printed pattern decorative laminates, to make use of a protective overlay sheet which is placed atop and is similar to the decorative sheet but is devoid of design and in the final laminate is transparent. The superimposed laminate components are then heat and pressure consolidated to a unitary structure. During the consolidation step, the thermosetting resins are converted to the thermoset state thereby providing an extremely hard, attractive and permanent laminated product. For obvious economic reasons, when producing the paper supported laminates, a plurality of these individual laminating assemblies are consolidated into one large assembly, each being separated from one another by a release sheet, and then to laminate this pack by heat and pressure application.
In consolidating the laminate components, an individual assembly is placed with its decorative overlayment surface adjacent to a highly polished stainless steel press plate. The plate provides a smooth, defect-free surface to one side of the laminate and also serves to separate pairs of back-to-back assemblies, thus permitting a plurality of these assemblies to be consolidated into laminates in one operation.
In the earliest days of the high pressure laminating art, the smooth, glossy surface produced during the pressing operation was sometimes, upon customer's request, reduced to a matte finish by rubbing the surface with pumice. Subsequently, a slightly textured surface was produced by pressing the laminate surface against an aluminum foil caul stock. Such a surface was described as mini-textured because the hilltop-to-valley bottom depth of such textures was from about 0.5 mil (0.0005 inches) to about 1.0 mil (0.001 inches). These mini-textured laminates met with immediate success and almost totally replaced the glossy surface market. Somewhat coarser textures or three dimensional surfaces, sometimes called "low-relief" laminates were then produced, e.g. by a printing process known as the "heavy ink" method, described in U.S. Pat. No. 3,373,068. These surfaces had hill-to-valley depths of about 3 to 5 mils.
Finally, very deep, three dimensional textured or embossed laminates were offered commercially. These laminates may be produced by e.g. the methods of U.S. Pat. No. 3,860,470, Jaisle etal., U.S. Pat. No. 3,718,496 Willard. Here the hill-to-valley depth in the surface is of the order of about 20 mils.
As demands for these new laminates grew, many new designs, such as those simulating tiles or heavy woven cloth, evolved. These designs must have appropriate color contrast and registry with the surface hill-to-valley configuration. The problem of registration of color and embossing proved very difficult to solve, not only from the standpoint of the appearance of the finished laminate but from the standpoint of the cost of the production of laminates having a substantially perfect registry of color and embossment. Embossed laminates have been successfully produced, however, and laminates of substantially registered color and embossment have also been prepared, see U.S. Pat. Nos. 4,091,198 and 4,092,199.
While the procedures disclosed in the above references have proven somewhat successful, the search for other methods for achieving registration of color and embossment has continued. In U.S. Pat. No. 4,093,766 there is disclosed a process whereby not only a registration of color and embossment is achieved but laminates having three different colors therein are disclosed.
The method disclosed in U.S. Pat. No. 4,093,766, while producing adequate laminates, functions by the flowing of pigment resins which are impregnated into paper sheets. Due to the difficulty of not only the impregnated resin but also the pigment particles to flow through the sheets during heat and pressure consolidation, the resultant laminates have not exhibited a degree of contrast of color which many desire.